Integrated circuits are made possible by processes which produce intricately patterned material layers on substrate surfaces. Producing patterned material on a substrate requires controlled methods of removal of exposed material. Chemical etching is used for a variety of purposes including transferring a pattern in photoresist into underlying layers, thinning layers or thinning lateral dimensions of features already present on the surface. Often it is desirable to have an etch process which etches a first material faster than a second helping, e.g., a pattern transfer process proceed. Such an etch process is said to be selective to the first material. As a result of the diversity of materials, circuits and processes, etch processes have been developed with a selectivity towards a variety of materials.
A SiConi™ etch involves the simultaneous exposure of a substrate to NF3 and NH3 plasma by-products and is largely conformal and selective towards silicon-containing layers, e.g. silicon, polysilicon and silicon dioxide. The SiConi™ etch can display other beneficial properties related to the mechanism by which material is processed on the surface of a substrate. The SiConi™ process produces solid by-products which grow on the surface of the substrate as substrate material is removed. The solid by-products are subsequently removed via sublimation when the temperature of the substrate is raised. One application of the SiConi™ etch is to remove thin native oxides (SiOx, x<2) formed on silicon-containing layers prior to further processing. Another application involves cleaning a processing chamber of silicon-containing process remnants.
The accumulation of solid by-products increasingly slow the penetration of the process into the layer resulting in the ability to precisely control the depth of processing or etch rate. Allowed to etch to a standstill, the SiConi™ etch becomes a “self-limiting” process. By varying some process parameters, each self-limiting cycle of exposure and anneal can be relied upon to remove a tunable and predictable amount of material.
The selectivity of existing SiConi™ processes have been established for silicon, polysilicon and silicon oxide. Incorporating carbon into silicon-containing layers results in silicon oxide has proven beneficial by decreasing the dielectric constant. Carbon content has also improved the gapfill of trenches by temporarily increasing the flowability of the film. Existing SiConi™ etch processes do not etch some of these silicon-and-carbon containing layers at etch rates high enough to be useful in production environments.